Heating elements have been used to fix toner to media in electrophotographic printing. Some fixing devices use a fixing member formed of one or more resistive heating elements enclosed in a halogen filled glass bulb and inserted into a cylinder formed of a thermally conductive material such as aluminum. The exterior surface of the cylinder has a release layer formed from a low adhesion material, such as TEFLON, to reduce toner adhesion to the surface. This embodiment of a fixing device is typically referred to as a halogen bulb fuser. Other fixing devices use a fixing member constructed of one or more flat resistive heating elements formed onto a ceramic substrate and surrounded by a sleeve made from a low adhesion flexible material. This embodiment of a fixing device is typically referred to as an instant on fuser.
For either a halogen bulb fuser or an instant on fuser, a backing member, such as a backing roller, rotates in contact with the surface of the fixing member. As media, having unfixed toner, moves between the fixing member and the backing roller, some of the toner may adhere to the surface of the fixing member even though it has a low adhesion coating.
The toner that adheres to the fixing member results in contamination of the backing roller by transfer of the toner from the fixing member to the backing roller. In a conventional fixing device, the surface temperature of the backing roller is lower than the surface temperature of the fixing member. As the backing roller rotates in contact with the fixing member, toner on the surface of the fixing member is cooled as it contacts the backing roller. The cooling of this toner causes it to adhere to the surface of the backing roller and pull away from the fixing member. Over time, significant amounts of toner can accumulate on the backing roller. The accumulated toner can break free and become fixed to the media resulting in a print defect on the media. A need exists for a fixing device that will reduce the severity of this type of print defect.